draft-ietf-mpls-cosfield-def-07.txt   draft-ietf-mpls-cosfield-def-08.txt 
Network Working Group L. Andersson Network Working Group L. Andersson
Internet-Draft Acreo AB Internet-Draft Acreo AB
Updates: RFC 3032, RFC 3270, RFC R. Asati Updates: RFC 3032, RFC 3270, RFC R. Asati
5129, RFC 3272, RFC 3443, RFC Cisco Systems 5129, RFC 3272, RFC 3443, RFC Cisco Systems
3469, RFC 3564, RFC 3985, RFC November 17, 2008 3469, RFC 3564, RFC 3985, RFC December 5, 2008
4182, RFC 4364, RFC 4379, RFC 4182, RFC 4364, RFC 4379, RFC
4448, RFC 4761 (if approved) 4448, RFC 4761 (if approved)
Intended status: Standards Track Intended status: Standards Track
Expires: May 21, 2009 Expires: June 8, 2009
"EXP field" renamed to "Traffic Class field" Multi-Protocol Label Switching (MPLS) label stack entry: "EXP" field
draft-ietf-mpls-cosfield-def-07.txt renamed to "Traffic Class" field
draft-ietf-mpls-cosfield-def-08.txt
Status of this Memo Status of this Memo
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Abstract Abstract
The early MPLS documents defined the form of the MPLS Label Stack The early Multiprotocol Label Switching (MPLS) documents defined the
entry. This include a three bit field called the "EXP field". The form of the MPLS Label Stack entry. This includes a three bit field
exact use of this field was not defined by these documents, except to called the "EXP field". The exact use of this field was not defined
state that it was to be "reserved for experimental use". by these documents, except to state that it was to be "reserved for
experimental use".
Although the intended use of the EXP field was as a "Class of Although the intended use of the EXP field was as a "Class of
Service" field, it was not named the "Class of Service" (CoS) field Service" (CoS) field, it was not named the CoS field by these early
by these early documents because the use of such a CoS field was not documents because the use of such a CoS field was not considered to
considered to be sufficiently defined. Today a number of standards be sufficiently defined. Today a number of standards documents
documents define its usage as a CoS field. . define its usage as a CoS field. .
To avoid misunderstanding about how this field may be used, it has To avoid misunderstanding about how this field may be used, it has
become increasingly necessary to rename this field. This document become increasingly necessary to rename this field. This document
changes the name of the field to the "Traffic Class field" ("TC changes the name of the field to the "Traffic Class field" ("TC
field".) In doing so it also updates documents that define the field".) In doing so it also updates documents that define the
current use of the EXP this field. current use of the EXP this field.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Details of change . . . . . . . . . . . . . . . . . . . . . . 5 2. Details of change . . . . . . . . . . . . . . . . . . . . . . 6
2.1. RFC 3032 . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. RFC 3032 . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. RFC 3270 . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2. RFC 3270 . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3. RFC 5129 . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3. RFC 5129 . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4. The Scope of this Change . . . . . . . . . . . . . . . . . 8 2.4. The Scope of this Change . . . . . . . . . . . . . . . . . 9
3. Use of the TC field . . . . . . . . . . . . . . . . . . . . . 10 3. Use of the TC field . . . . . . . . . . . . . . . . . . . . . 11
4. IANA considerations . . . . . . . . . . . . . . . . . . . . . 11 4. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12
5. Security considerations . . . . . . . . . . . . . . . . . . . 12 5. Security considerations . . . . . . . . . . . . . . . . . . . 13
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Normative References . . . . . . . . . . . . . . . . . . . 14 7.1. Normative References . . . . . . . . . . . . . . . . . . . 15
7.2. Informative references . . . . . . . . . . . . . . . . . . 15 7.2. Informative references . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 17 Intellectual Property and Copyright Statements . . . . . . . . . . 18
1. Introduction 1. Introduction
The format of a MPLS label stack entry is defined by RFC 3032 The format of a MPLS label stack entry is defined by RFC 3032
[RFC3032], include a three bit field called the "EXP field". The [RFC3032], include a three bit field called the "EXP field". The
exact use of this field is not defined by RFC 3032 leaves, except to exact use of this field is not defined by RFC 3032 leaves, except to
state that it is to be "reserved for experimental use". state that it is to be "reserved for experimental use".
The EXP field, from the start, was intended to carry "Class of The EXP field, from the start, was intended to carry "Class of
Service" information. The field was actually called the "Class of Service" (CoS) information. The field was actually called the "Class
Service field" in the early versions of the working group document of Service field" in the early versions of the working group document
that was publshed as RFC 3032. However at the time that RFC 3032 was that was published as RFC 3032. However at the time that RFC 3032
published the exact usage of this "Class of Service" field was not was published the exact usage of this "Class of Service" field was
agreed and the field was designated as "Experimental use". not agreed and the field was designated as "Experimental use"; hence
the name has since then been the "EXP Field".
The designation "for Experimental use" has led other Standards The designation "for Experimental use" has led other Standards
Development Organizations (SDO) and implementors to the assume that Development Organizations (SDO) and implementors to the assume that
it possible to use the field for other purposes. This document it possible to use the field for other purposes. This document
changes the name of the field to clearly indicate its use as a changes the name of the field to clearly indicate its use as a
traffic classification field. traffic classification field.
At first we discussed to use the original "CoS field" as the name for At first we discussed to use the original "CoS field" as the name for
the field, but it has been pointed that this name does not cover the the field, but it has been pointed that this name does not cover the
following changes wrt its usage, since RFC 3032 was published. following changes with respect to its usage, since RFC 3032 was
published.
1. The use of the EXP field was first defined in RFC 3270 [RFC3270] 1. The use of the EXP field was first defined in RFC 3270 [RFC3270]
where a method to define a variant of DiffServ LSPs called EXP- where a method to define a variant of DiffServ Label Switched
Inferred-PSC LSP (E-LSPs) was specified. Paths (LSP) called EXP-Inferred-PSC LSP (E-LSPs) was specified.
The PSC is a two stage acroynym that is expanded as Per Hop
Behavior (PHB) and PHB Scheduling Class (PSC).
2. The use of the EXP field as defined in RFC 3270 has been further 2. The use of the EXP field as defined in RFC 3270 has been further
extended in RFC 5129 [RFC5129], where methods for explicit extended in RFC 5129 [RFC5129], where methods for explicit
congestion marking in MPLS are defined. congestion marking in MPLS are defined.
This document, hence, uses the name "Traffic Class Field (TC Field)", This document, hence, uses the name "Traffic Class Field (TC Field)",
which better covers the potential use. The MPLS TC field relates to which better covers the potential use. The MPLS TC field relates to
an MPLS encapsulated packet the same way as the IPv6 TC field relates an MPLS encapsulated packet the same way as the IPv6 TC field relates
to an IPv6 encapsulted packet or the IPv4 Precedence field relates to to an IPv6 encapsulted packet or the IPv4 Precedence field relates to
an IPv4 encapsulated packet. an IPv4 encapsulated packet.
The defintions of how the EXP field are used are perfectly clear in The definitions of how the EXP field is used are perfectly clear in
RFC 3270 and RFC 5129. However, these RFCs do not explicitly state RFC 3270 and RFC 5129. However, these RFCs do not explicitly state
they update RFC 3032, and this fact is not captured in the RFC they update RFC 3032, and this fact was not captured in the RFC
respository. This document updates RFC 3032, RFC 3270 and RFC 5129 repository until after the work on this document were started. This
to clarify the intended usage of the TC field. Section 2 explains document updates RFC 3032, RFC 3270 and RFC 5129 to clarify the
the changes. intended usage of the TC field. Section 2 explains the changes.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Details of change 2. Details of change
The three RFCs are now updated according to the following. The three RFCs are now updated according to the following.
2.1. RFC 3032 2.1. RFC 3032
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label
| Label | TC |S| TTL | Stack | Label | TC |S| TTL | Stack
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry
Label: Label Value, 20 bits Label: Label Value, 20 bits
CoS: Traffic Class field, 3 bits CoS: Traffic Class field, 3 bits
S: Bottom of Stack, 1 bit S: Bottom of Stack, 1 bit
TTL: Time to Live, 8 bits TTL: Time to Live, 8 bits
Figure 1 Figure 1 (new)
Note: The designation of the picture above as "Figure 1 new" is
introduced as a way to distinguish the figures in this draft. It
will still be "Figure 1." in RFC 3032.
2.2. RFC 3270 2.2. RFC 3270
RFC 3270 says on page 6: RFC 3270 says on page 6:
1.2 EXP-Inferred-PSC LSPs (E-LSP) 1.2 EXP-Inferred-PSC LSPs (E-LSP)
A single LSP can be used to support one or more OAs. Such LSPs A single LSP can be used to support one or more OAs. Such LSPs
can support up to eight BAs of a given FEC, regardless of how many can support up to eight BAs of a given FEC, regardless of how many
OAs these BAs span. With such LSPs, the EXP field of the MPLS OAs these BAs span. With such LSPs, the EXP field of the MPLS
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This is an update to RFC 3032 [RFC3032] in line with the original This is an update to RFC 3032 [RFC3032] in line with the original
intent of how this field in the MPLS Shim Header should be used intent of how this field in the MPLS Shim Header should be used
(as TC field). The RFC 3270 has itself been updated by RFC 5129 (as TC field). The RFC 3270 has itself been updated by RFC 5129
[RFC5129]. [RFC5129].
Detailed operations of E-LSPs are specified in section 3 of Detailed operations of E-LSPs are specified in section 3 of
RFC3270. RFC3270.
2.3. RFC 5129 2.3. RFC 5129
RFC 5129 is now updated like this:
A new paragraph is added at the end of section 1.1 "Background":
The EXP field has been renamed to the TC field, and thus all
references in RFC 5129 to EXP field SHOULD be taken to refer to
the TC field.
Section 2 (bullet 3) on page 6 of RFC 5129 says: Section 2 (bullet 3) on page 6 of RFC 5129 says:
o A third possible approach was suggested by [Shayman]. In this o A third possible approach was suggested by [Shayman]. In this
scheme, interior LSRs assume that the endpoints are ECN-capable, scheme, interior LSRs assume that the endpoints are ECN-capable,
but this assumption is checked when the final label is popped. If but this assumption is checked when the final label is popped. If
an interior LSR has marked ECN in the EXP field of the shim an interior LSR has marked ECN in the EXP field of the shim
header, but the IP header says the endpoints are not ECN-capable, header, but the IP header says the endpoints are not ECN-capable,
the edge router (or penultimate router, if using penultimate hop the edge router (or penultimate router, if using penultimate hop
popping) drops the packet. We recommend this scheme, which we popping) drops the packet. We recommend this scheme, which we
call `per-domain ECT checking', and define it more precisely in call `per-domain ECT checking', and define it more precisely in
the following section. Its chief drawback is that it can cause the following section. Its chief drawback is that it can cause
packets to be forwarded after encountering congestion only to be packets to be forwarded after encountering congestion only to be
dropped at the egress of the MPLS domain. The rationale for this dropped at the egress of the MPLS domain. The rationale for this
decision is given in Section 8.1. decision is given in Section 8.1.
RFC 5129 is now updated like this: Section 2 (bullet 3) of RFC 5129 is now updated changed to:
A new paragraph is added at the end of section 1.1 "Background":
The EXP field has been renamed to the TC field, and thus all
references in RFC 5129 to EXP field SHOULD be taken to refer to
the TC field.
Section 2 (bullet 3) on page 6 is now changed to:
o A third possible approach was suggested by [Shayman]. In this o A third possible approach was suggested by [Shayman]. In this
scheme, interior LSRs assume that the endpoints are ECN-capable, scheme, interior LSRs assume that the endpoints are ECN-capable,
but this assumption is checked when the final label is popped. If but this assumption is checked when the final label is popped. If
an interior LSR has marked ECN in the TC field of the shim header, an interior LSR has marked ECN in the TC field of the shim header,
but the IP header says the endpoints are not TC-capable, the edge but the IP header says the endpoints are not TC-capable, the edge
router (or penultimate router, if using penultimate hop popping) router (or penultimate router, if using penultimate hop popping)
drops the packet. We recommend this scheme, which we call `per- drops the packet. We recommend this scheme, which we call `per-
domain ECT checking', and define it more precisely in the domain ECT checking', and define it more precisely in the
following section. Its chief drawback is that it can cause following section. Its chief drawback is that it can cause
packets to be forwarded after encountering congestion only to be packets to be forwarded after encountering congestion only to be
dropped at the egress of the MPLS domain. The rationale for this dropped at the egress of the MPLS domain. The rationale for this
decision is given in Section 8.1. This scheme is an update to RFC decision is given in Section 8.1. This scheme is an update to RFC
3032 [RFC3032] and RFC 3270 [RFC3270]. 3032 [RFC3032] and RFC 3270 [RFC3270].
2.4. The Scope of this Change 2.4. The Scope of this Change
There are several places in the RFCs that has explicitly updated by There are several places in the RFCs that has explicitly updated by
this document that refrence the "Exp field", sometimes they refer to this document that reference the "Exp field", sometimes they refer to
the field as "Exp bits", "EXP bits" and "EXP". In all those the field as "Exp bits", "EXP bits" and "EXP". In all those
instances the references SHOULD be taken to reference the TC field. instances the references SHOULD be taken to reference the TC field.
There are also other RFCs, e.g. RFC 3272 [RFC3272], RFC 3443 There are also other RFCs, e.g. RFC 3272 [RFC3272], RFC 3443
[RFC3443], RFC 3469 [RFC3469], RFC 3564 [RFC3564], RFC 3985 [RFC3443], RFC 3469 [RFC3469], RFC 3564 [RFC3564], RFC 3985
[RFC3985], RFC 4182 [RFC4182], RFC 4364 [RFC4364], RFC 4379 [RFC3985], RFC 4182 [RFC4182], RFC 4364 [RFC4364], RFC 4379
[RFC4379], RFC 4448 [RFC4448] and RFC 4761 [RFC4761] that references [RFC4379], RFC 4448 [RFC4448] and RFC 4761 [RFC4761] that references
the "Exp field", sometimes they refer to the field as "Exp bits", the "Exp field", sometimes they refer to the field as "Exp bits",
"EXP bits" and "EXP". For all RFCs, including but not limited to "EXP bits" and "EXP". For all RFCs, including but not limited to
those mentioned in this paragraph, such references SHOULD be taken to those mentioned in this paragraph, such references SHOULD be taken to
skipping to change at page 11, line 7 skipping to change at page 12, line 7
rewrite all or some of the bits in the TC field. rewrite all or some of the bits in the TC field.
Current implementations look at the TC field with and without label Current implementations look at the TC field with and without label
context and the TC field may be copied to the label stack entries context and the TC field may be copied to the label stack entries
that are pushed onto the label stack. This is done to avoid that that are pushed onto the label stack. This is done to avoid that
label stack entries that are pushed on to an existing label stack label stack entries that are pushed on to an existing label stack
have different TF fields from the rest of the label stack entries. have different TF fields from the rest of the label stack entries.
4. IANA considerations 4. IANA considerations
There are no request for IANA allocation of code points in this There are no requests for IANA allocation of code points in this
document. document.
5. Security considerations 5. Security considerations
This document only changes the name of one field in the MPLS Shim This document only changes the name of one field in the MPLS Shim
Header and thus does not introduce any new security considerations. Header and thus does not introduce any new security considerations.
6. Acknowledgments 6. Acknowledgments
The author would like to thank Stewart Bryant, Bruce Davie, George The author would like to thank Stewart Bryant, Bruce Davie, George
 End of changes. 17 change blocks. 
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